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The fall of Mosul and Tikrit to ISIS is a wake-up call to all the states of the region: It’s time to put an end to the Syrian civil war and the sectarian mayhem it has spawned.

The fall of Mosul (and now Tikrit) to the Islamic State of Syria and Iraq (ISIS), an al-Qaeda affiliate, is fallout of a new and shocking sort from the Syrian civil war. Even if ISIS’s occupation turns out to be both partial and temporary, like Ansar al-Din’s occupation of Timbuktu some months ago, it represents a colossal setback for all the actors in the region, even if some of those actors are at odds with others. This is because ISIS represents the ultimate in radicalization, and yet it was able to launch and sustain a fairly sophisticated military operation against the second largest city in Iraq. When a non-state actor can do that in the face of state collapse in both Syria and Iraq, it is clear that reverberations will remain with the region and the world at large for a long time to come. In the meantime, violence, some of it truly unspeakable, is very likely about to visit the people of Mosul and its environs, with refugees once again streaming across borders.

The quick fall of Mosul should be a clarion call for the states of the region: The time has come to put an end to the Syrian civil war, which has spawned or strengthened violent Sunni jihadists and their Shi’a counterparts throughout the region. The West, and particularly the Obama Administration, has made it clear that it will not intervene militarily on the ground. One of the reasons for this reluctance from the start (though certainly not the only reason) was the concern that in a chaotic situation U.S. weapons might end up in the wrong hands. After ISIS took possession of all kinds of weapons from haphazardly retreating U.S.-trained Iraqi soldiers, Washington will be even more reticent to supply advanced arms to any kind of opposition in Syria. What this means is that states in the region will have to take the lead in putting the Syrian civil war out of its misery.This seems unlikely, true. But what has happened in Mosul may change the situation. The shocking events in Mosul mark another in a series of nasty blowbacks. Iraqi jihadis engaged the regime in Baghdad and the moderate opposition in Syria in search of ways to leverage their small forces into a larger ambit of influence, and their interlocutors complied—only to have ISIS turn around and occupy Mosul. Iran, Turkey, and Saudi Arabia are the three most important actors in this drama, however, not Iraq or anyone in Syria. All three in different ways contributed to these events, because they all funded and trained extremists. Some extremists who used to fight with Jabat al-Nusra, when Turkey was helping that group, may now be in the hire of ISIS. But all three countries, and Qatar and others as well, now stand to be victimized by the monsters they helped create.Indeed, the deepening of the sectarian divide is not in the interest of any of these three regional powers. Iran, which has approached the Syrian crisis from the perspective of trying to defend its alliance, comprised of Hizballah in Lebanon, Assad in Damascus, and Iraqi Prime Minister Nouri al-Maliki in Baghdad, will realize sooner or later that even if Assad remains in power it will not make Iran safe from the mayhem it has helped to create. That sectarian mayhem will continue to undermine Tehran’s allies and do nothing to relieve its isolation, notwithstanding the P5+1/Iran nuclear negotiations. Worse, from the Iranian point of view, if Iraq were to succumb to a Syria-like civil war, Iran would possibly find that its own borders were no longer inviolable.Frustrated by Assad’s resilience, Turkey flirted with al-Nusra, another of the al-Qaeda groups in Syria, but has now come to the realization that the jihadis in Syria represent a direct security threat to its own citizens and what is left of the regional order, including the stability of the Kurdistan Regional Government upon which much of its recent strategic/diplomatic efforts have been focused. The Turkish leadership is now cooperating with Western security establishments to identify and catch foreign jihadis that used its territory to enter Syria.The Saudis should also be worried—and after all they are very well practiced at it. They may dislike the Iranians and their Shi‘a ways, but, as they should have learned long ago from al-Qaeda’s founder Osama bin Laden, they are in the crosshairs of the jihadi threat. They banned the Muslim Brotherhood lately, but no country’s citizens, if not also the state, have done more to foment radical Islam over the past four decades than those of Saudi Arabia. Saudi Arabia also stands to lose much if Jordan, a close Saudi ally and buffer state already suffering from the strain of Syrian refugee flows, becomes ISIS’s next target.Coincidentally, the fall of Mosul occurred during Iranian President Rouhani’s visit to Turkey. Despite the fact that they are deeply engaged on opposite sides of the Syrian conflict, the two countries have agreed to disagree. The reason is simple: They have other important shared interests, such as oil and gas trade and political support for the Iranian nuclear program. Considering Syria’s importance to both regimes, perhaps Turkish-Iranian pragmatism can be bent in the direction of agreement to construct a transitional arrangement for Syria? Both now need face-saving policy options. The trick is to come up with an interim deal that includes Assad’s departure, though perhaps not immediately, in exchange for the safeguarding of some core Iranian interests in a future Syrian political system.This may sound improbable, and it is. Nonetheless, the fall of Mosul shows that the Syria crisis, which was almost from the beginning an Iraqi crisis as well, requires a regional solution. The Obama Administration was right not to intervene directly in Syria with military force, but wrong to construe its options as either war-making or what amounts to passivity. The perception of Washington policymaking in Syria as dithering and less-than-professional has arguably spread throughout the region. The Administration can begin to reverse this image if it is willing to encourage the region to come up with its own solution. That effort would have to start in consultation with Turkey and Saudi Arabia, and it would have to include Iran as well in the end.Maybe in Syria, Washington is once again ready to lead from behind?

Henri J. Barkey is a professor of international relations at Lehigh University.